OBJECTIVE: The resource consists of unique inbred lines, linkage and mutant stocks and certain inbred lines. These are used for research within the center and are available to investigators elsewhere on request. APPROACH: The effect of the r-chromosome on sex ratio and male behavior using PHH and PHL mice, also PHHYL and PHLrH is being investigated. The primary sex ratio is being determined in first cleavage embryos. A number of reproductive characters in mice homozygous or heterozygous for p-sterile and p-fertile alleles are under study including ability of sterile males to copulate, inducement of pseudopregnancy in semi sterile females, and sperm head morphology in sterile males. The following parameters are being investigated using R.I.A.: Blood plasma LH and FH levels, pituitary LH and FSH content.